Finding harvest mouse nests isn’t rocket science: all you need to do is keep an eye out for suitable habitat and then dive in! If a tussock of grass has the potential to hide a tennis ball, then there could be a nest inside.
Harvest mice make spherical nests out of long pieces of woven grass above ground level. They like a range of plants in which to build their nests, but in Devon the majority of nests are found in tussocks of Cocksfoot grass, Molinia and Phragmites (common reeds). They make tennis-ball sized nests for breeding, and ping-pong ball sized nests as nests for individuals. The nests start off the same colour as the summer vegetation, and fade to brown as they age. Females build breeding nests over a couple of days by shredding stems of grass weaving them around vertical stems. This means that they can’t blow out with the wind or fall out if knocked. Harvest mice only use grasses/shredded Phragmites as a building material, so you won’t find moss or leaves in the construction. You can click here to see a flow chart to help identify a nest.
If it’s a harvest mouse nest, do please send in a record as we’re trying to locate where they are across the county. If you’re not in Devon, the National Harvest Mouse Survey would love to know where it was.
If you find a green nest (or one with green grass in it) you should cover it back up and walk away as it is likely to be in use. You can also find occupied brown nests but it is far less likely.
The video below will show you how to look for nests.